Modern passenger transport aircraft typically operate at elevated altitudes in order to avoid weather and to obtain other significant advantages generally associated with high altitude flight. Accordingly, such aircraft are equipped with an environmental control system that provides pressurized and temperature controlled air to passengers within a cabin of the aircraft. Briefly and in general terms, the environmental control system typically extracts air at an elevated temperature and pressure from a compressor section of one or more of the engines of the aircraft, suitably conditions the extracted air and distributes the conditioned air to the cabin to provide a comfortable environment for the flight crew and passengers within the aircraft.
The suitably conditioned air is continuously supplied to various portions of the aircraft cabin through an air distribution system. Typically, the aircraft cabin includes a flight deck area that is occupied by a flight crew, a passenger compartment that is occupied by the passengers, and one or more cargo compartments that are occupied by cargo items, such as passenger luggage, freight items, or other like items. In general, the environmental control system provides air to the various portions of the aircraft cabin according to a predetermined air distribution plan. For example, the flight deck area may be provided with substantially outside air, while the passenger compartment receives a reduced volume of outside air that is mixed with recirculated and filtered air previously within the passenger compartment so that the resulting air mixture includes both outside air and highly filtered air portions. Typically, the mixture in the passenger cabin is continuously maintained at approximately about one-half outside air by volume. The cargo compartment receives air from various sources that may include outside air, or recirculated air. In some cases, the cargo compartment is not ventilated, so that it does not receive air. In any case, a selected volume of the air within the cargo compartment is released to the lower lobe cheek region and discharged from the aircraft through an outflow valve that is controllable by the environmental control system and/or discharged through other means, such as through cabin and/or cargo door leakage.
The air temperature within the flight deck and the passenger compartment are generally closely regulated to achieve a desired comfort level to the flight crew and the passengers. Accordingly, the flight deck and the passenger compartment generally include various temperature sensing devices positioned in flight deck and passenger compartments that are operable to control the system to admit additional cold air when additional cooling is desired, and to correspondingly add additional higher temperature air when additional heating is desired.
The air temperature within the cargo compartment is generally controllable within wider temperature ranges so that the cargo compartment may accommodate a variety of different cargo items. For example, when perishable cargo is contained within the cargo compartment, lower air temperatures are generally preferred, while somewhat warmer air temperatures are preferred when live cargo is transported within the cargo compartment.
One shortcoming associated with current environmental control systems is that they may provide only for the addition of heat into the cargo compartment by continuously moving air into the cargo compartment, or from the lower lobe cheek into the compartment. Alternately, air within the compartment may be moved through one or more electrical resistance heaters to provide additional heat to the cargo compartment. In still another method, hot outside air from the compressor section of one or more of the engines may be introduced into the compartment. Accordingly, removing heat from cargo compartment air is achievable only by passive means (e.g., by conducting heat through an outer skin of the aircraft). In order to attain better temperature control, conditioned air may be supplied to the cargo compartment from the cabin and/or flight deck supply systems. Since this approach generally increases the outside air requirement, fuel consumption is disadvantageously increased.
What is needed in the art is an environmental control system that permits air temperatures within a selected compartment, such as a cargo compartment, to be controlled in a manner that is energy efficient, avoids the addition of weight to the aircraft and that minimizes the outside air requirement.